The present invention refers to a device for controlling a hydrostatic drive having a resonator which is connected on the one hand to the hydrostatic drive and, on the other hand, to a pressurized-fluid supply line and a return line, and having a periodically actuatable switch valve which connects the resonator alternately with the pressurized-fluid supply line and the return line.
In order to avoid, in particular, the throttle losses of throttle-controlled hydrostatic drives, it is known not to connect the drive continuously via a throttle valve but rather periodically to a hydraulic-fluid supply line or a return line over switch valves each connected in parallel with a non-return valve. The opening of the switch valve in the hydraulic-fluid supply line results in an accelerating of the drive, the inertia of which upon the closing of this switch valve leads to a reduction in the pressure of the compressible hydraulic fluid in the drive region to a pressure which is less than the closure pressure of the non-return valve in the region of the return line so that, via the return line, hydraulic fluid can be drawn in until the switch valve in the supply line again opens and the process is repeated. In the event of a useful braking of the drive there results, upon the closing of the switch valve in the return line, an increase in the pressure of the drive-side hydraulic fluid to an amount exceeding the closing pressure of the non-return valve in the region of the supply line, which brings about a pumping of the hydraulic fluid back into the supply line. This additional flow of hydraulic fluid made possible by the pulsating control of the drive brings about a corresponding recovery of energy and thus an improved efficiency which, to be sure, is purchased at the cost of a comparatively slight dynamism and a corresponding structural expense.
In order to adjust the operating pressure for the hydrostatic drive independently of its operating path between the maximum pressure offered by the hydraulic-fluid supply line and the pressure of the return line, it has already been suggested that the hydrostatic drive be connected to a resonance tube which is connected alternately via a periodically actuatable switch valve to a pressurized-fluid supply line and a return line in order to produce standing pressure waves of the hydraulic fluid in the resonance tube under conditions of resonance. By the provision of a pressure outlet in an oscillation node of the resulting standing pressure waves in the resonance tube, it is possible to provide at this pressure outlet an operating pressure for the drive via the operating path of the drive. Furthermore, the pressure waves of the arrangements associated with this node at the pressure outlet are suppressed so that, despite a pulsating control, the pulsation in time of the operating pressure at the pressure outlet is comparatively slight. Since the length of the resonance tube must be selected as a function of the length of the pressure waves formed in the hydraulic fluid, corresponding tube lengths are to be expected which may limit the possible use of these devices. Furthermore, due to the pressure adjustment, such a device is advisable for the adjustment of the pressure, in particular for the acceleration control.